1. Technical Field
The present invention relates to a pigment dispersion, ink composition, ink set, and recording device, and particularly relates to a pigment dispersion, ink composition, ink set, and recording device which can form an image with metallic gloss.
2. Related Art
Conventionally, gold bronze powder made of brass and aluminum fine powders and the like, printing ink with silver powder pigment, foil press printing using metal foil, and a thermal transfer method using a metal foil have been used to form a coating film with metallic gloss of printed matter.
However, with a coating film consisting of a printing ink that uses gold bronze powder, or silver powder, the average particle size of the metal powders that are used will be large, between 10 μm and 30 μm, and thus a flat metallic gloss finish can be obtained, but achieving a mirror gloss is difficult. Furthermore, with the foil press or thermal transfer methods that use a metallic foil, an adhesive is applied as a printing medium, and a flat metallic foil is pressed thereon, the recording medium and the metallic foil are heated to cause firm adhesion, and the metal foil and recording medium are thermally welded together. Therefore, a relatively good gloss can be achieved, but there are many manufacturing steps, and pressure and heat are applied during the manufacturing process, so the recording medium is restricted to the limited recording media that are resistant to heat and deformation.
In recent years, many examples of applying inkjet technology to printing have been seen, and one example of this application is metallic printing. For example, JP-A-2002-179960 discloses technology of forming a metal film on the surface of plastic spherical particles, and printing an ink composition that contains a pigment using inkjet printing. However, in order to obtain a highly metallic gloss, the spheres must be deformed and flattened to make a smooth surface, and with this technology, heating and pressing with a roller must be simultaneously performed. Therefore, the equipment and manufacturing processes are inevitably complicated by this point, and the recording medium is also restricted.
Furthermore, JP-A-2003-292836 and JP-A-2003-306625 disclose technology that uses an ink composition wherein a colloid of a precious metal such as gold or silver is dispersed. However, if the particle size of the precious metal colloid is small, within a range between several nanometers and several tens of nanometers in order to give priority to dispersion and stability, discoloration caused by plasmon absorption will occur, and the ink composition will not provide a metallic gloss. In this case, after the coating film is dried, a metallic gloss is achieved by heating to a temperature of 150° C. or higher in order to fuse the colloid particles together. In addition, even if a metallic gloss can be achieved with these technologies, achieving a surface with a mirror surface metallic gloss where the specular gloss at 20°, 60°, and 85° exceeds 200, 200, and 100, respectively on a uniform surface without variation is difficult. Furthermore, if the particle size is increased in order to give priority to metallic gloss, the dispersion stability will be degraded, and problems with conglomeration and settling will be inevitable, and the storage life of the ink composition will be significantly reduced. Furthermore, although trivial, using precious metals as a material will increase the cost of the ink composition, so use will be restricted to applications with high added value, and there are disadvantages related to cost.